1. Field of the Invention
This invention relates to an improved gauge assembly for monitoring the level of fluid in a storage tank or like container, and to an improved, convenient method for installing such a gauge assembly.
2. Description of the Prior Art
A great variety of devices have been used to determine and provide indications of the liquid level in storage tanks and other such vessels. However, monitoring the level of storage tanks which contain petroleum products or other volatile liquids presents special requirements that have not been fully satisfied by the technology which is in common use today.
Petroleum products such as oil and gasoline contain viscous components which tend to coat any surface which is exposed to them. This effectively precludes the use of visual sight gauges for fluid level monitoring. The volatile nature of such fluids also makes their monitoring with electronic level sensing equipment more dangerous and otherwise problematic.
Float level gauges have been used in the past to monitor the level of petroleum based products. Such a gauge is disclosed in U.S. Pat. No. 3,482,447 to Bennett. This device includes an analog gauge that is synchronized with an internal drum. Wrapped about the drum is a gauge line that is connected to a float element. The drum is biased in a first rotary direction by an elongated coil-type spring, which keeps the gauge line in tension. As the float element rises or falls in response to the level of the liquid within a storage tank, the analog display reflects the resultant rotation of the drum.
Mechanically, this type of gauge has proven effective for monitoring the fluid level for petroleum base products. However, the installation of such gauges can be relatively difficult, particularly in storage tanks which are already filled. The Bennett gauge, for example, is apparently intended to be mounted to a storage tank by a flange which is bolted onto the tank. To mount such a flange, holes need to be drilled into the outer wall of the tank. The float needs to be introduced into the tank, and then connected to the gauge line. The gauge line, due to the tension exerted on it by the spring biased drum, is likely to completely retract into the housing of the gauge during this process, thereby exacerbating the difficulty of installation.
It is particularly important that installation time be kept to a minimum while working on tanks which are already in operation, due to the possible release of volatile and toxic vapors from the tank while the tank is open to atmosphere.
It is also important that a gauge be quickly and easily calibrated to reflect the liquid level within a tank after it is installed. In an analog gauge, this requires the position of the indicating hands to be mechanically adjustable. It is important, however, that such adjustability not be achieved at the expense of reducing the vapor tightness of the gauge housing, which is essential to avoid releasing vapor into the atmosphere.
It is clear that there has existed a long and unfilled need in the prior art for a liquid level gauge which is convenient to install, which can be quickly calibrated to reflect the level of liquid within a storage tank to which it is mounted, which is mechanically simple and inexpensive to manufacture, and which protects the environment against escape of vapors from the storage tank.